In general, in the optical recording media, there are a ROM type for read only, a WORM type for writing once, and a rewritable type for repetitive writing. In the ROM type optical recording media, there are CD-ROM (Compact Disc Read Only Memory), DVD-ROM (Digital Versatile Disc Read Only Memory) and the like, and, in the WORM type optical recording medium, there are CD-R (Recordable Compact Disc) which permits one time writing, DVD-R (Recordable Digital Versatile Disc) which permits one time writing, and the like. And, in disks which are rewritable freely and repetitively, there are CD-RW (Rewritable Compact Disc), and rewritable digital versatile disc (DVD-RAM, DVD-RW).
In rewritable optical disks, information writing/reading thereto/therefrom is done repetitively. The repetitive write/read of information causes a change in a ratio of components, i.e., the mixture, that form a recording layer (provided for recording information), from an initial mixing ratio. This leads to a loss in the initial properties of the mixture, and that causes errors to occur in writing/reading information. This overall process is called degradation.
Areas of degradation are identified as defective areas when formatting, or when executing a write or read command for the optical disk. Other than by degradation, defective areas of the rewritable optical disk are caused by scratch on a surface, dust particles, and/or from production defects. To prevent writing/reading data to/from the defective areas formed by the foregoing causes, management of the defective areas is required.
As shown in FIG. 1, DMA's (Defect Management Areas) are provided in a lead-in area and in a lead-out area of the optical recording medium for managing the defective areas of the optical recording medium. Data areas are managed in zones (or groups), each having a user area for use in actual writing of data and a spare area to prove replacement capacity in the case of defects in the user area. In general, there are four DMAs provided in one disk (for example, a DVD-RAM), two in the lead-in area and the other two in the lead-out area.
As management of the DMAs is important, the same data is repeatedly written in the four DMAs for its protection. Each DMA has two blocks having 32 sectors in total, i.e., one block has 16 sectors. Each DMA has a PDL (Primary Defect List) which is a primary data storage and an SDL (Secondary Defect List) which is secondary data storage. In general, the PDL contains entries of defects that occurred during fabrication of the disk, and all defective sectors identified during formatting, i.e., initializing and re-initializing, of the disk. On the other hand, the SDL, which is organized in block units, contains entries of defective areas that occurred after the formatting, or defective areas that cannot be listed on the PDL during the formatting. The defective areas (i.e., defective sectors or defective blocks) in the data area are replaced with good areas, according to a slipping replacement algorithm or linear replacement algorithm.
FIG. 2A depicts a circumstance in which the slipping replacement algorithm is applied to a defective area listed on the PDL. If the defective sector is present in the user area on which actual data is to be written, then the defective sector is skipped. The defective sector is replaced with a good sector next to the defective sector.
FIG. 2B depicts a circumstance in which the linear replacement algorithm is applied to a defective area listed on the SDL. If the defective block is present in the user area or the spare area, then the defective block is replaced with block units of replacement areas assigned to the spare area.
FIG. 3 illustrates a block diagram showing one example of a recording portion of a related art optical recording medium recording/reproduction device. It is provided with an optical pickup for writing/reading data to/from an optical recording medium, a pickup servo unit for controlling the optical pickup to maintain a distance between an objective lens in the optical pickup and the optical disk and for tracking a pertinent track, a data processor for processing and providing an input data to the optical pickup, an interface for exchanging data with an external host, and a microcomputer for controlling the above units. A host is connected to the interface of the device for recording/reproducing data to/from an optical recording medium for exchange of command and data.
Referring to FIG. 4, when data to be written is provided to the host, the host then provides the data to be written together with a write command to the device for recording/reproducing data to/from an optical recording medium. In this instance, the device for recording/reproducing data to/from an optical recording medium writes no data on defective areas utilizing the PDL and the SDL. That is, physical sectors listed on the PDL are skipped in the writing. As shown in FIG. 4, physical blocks b1kA and b1kB (listed on the SDL) are replaced with replacement blocks b1kE and b1kF assigned to the spare area in the writing. If a defect occurs again in a replacement block b1kG (that was intended to replace the defective block b1kC), a new replacement block b1kH in the spare area is assigned to the defective block b1kC for writing the data. And, during a writing or reading operation, if a defective block is discovered that is also not listed on the SDL, then a replacement block is located in the spare area, the data on the defective block is written thereon again, and positional information on the defective block are listed on the SDL entry for protection of the data. Instead of a defective block, if a block having a high possibility of causing an error is discovered during a writing or reading operation, then this block is treated as if it were a defective block in the manner just described. Thus, not only blocks with defects, but also blocks with a high possibility of causing errors, for example, blocks error thereon can be corrected are subjected to linear replacement, for protection of data.
However, the aforementioned DVD-RAM has the problem of a reduced recording capacity caused by the spare areas allocated in a disk fabrication process for protection of data. And, because the size of the spare areas are fixed in advance without regard to the actual defective state of the disk, the spare areas are used inefficiently. In most instances, the disk management technique will not use entire spare areas. Also, if the total number of defective sectors for a block is larger than the total number of spare areas, all of the defective sectors cannot be replaced. This causes the disk management technique to fail. In this instance, the system will treat the disk as fatally defective, and the disk will no longer be used.
A CD-RW is one of the rewritable optical recording media. It manages defective sectors only when the defect is fatal, but does not manage correctable errors. The data protection provided by the CD-RW is not adequate.